This invention is directed to an improved intake valve mechanism for an internal combustion engine and particularly to a back-flow valve designed to prevent gases in a combustion chamber from being blown back into an air-fuel intake port of the chamber and yet not impede the normal flow of air-fuel mixture passing into the chamber through the intake port.
In some four cycle internal combustion engines, intake and exhaust valves to the combustion chamber are both kept open simultaneously for a certain period in order to increase exhaust efficiency of the engine. However, as a consequence of both valves being open simultaneously, part of the exhaust gases burnt in the combustion chamber are blown past the open intake valve and back into the intake passage of the engine where the exhaust gases are mingled with the air-fuel mixture flowing through the intake passage during the next engine cycle. The exhaust gases impair ignition of the air-fuel mixture and therefore act to make the entire combustion operation of the engine unstable. The instability and accompanying inefficiency are particularly acute in the medium to low speed operational ranges of the engine and during idling of the engine.
In addition, modern internal combustion engines which are adapted to burn lean air-fuel mixtures in order to decrease the amount of toxic substances usually present in the engine exhaust gas, demand strict control of the air-fuel ratio. In this type of engine, the mingling of exhaust gas with the air-fuel mixture in the intake passage of the engine creates an even more acute operational deficiency.
The undesirable back-flow of gases from the combustion chamber to the intake passage is not limited to only the overlap period when both intake and exhaust valves are open. Back-flow can also occur when the intake valve is phased to close slightly behind the time at which the piston reaches bottom dead center of its cycle in order to raise the intake efficiency of the engine in its high speed operational range. In the medium to low speed range, fresh air-fuel mixture which enters the combustion chamber before the piston reaches the bottom dead center is forced back through the intake passage during the time when the piston passes bottom dead center and the intake valve remains open. The result is that in the medium to low speed range the intake efficiency of the engine is lowered instead of being improved.
The problem of gas back-flow is not limited to four cycle internal combustion engines. Even in a two cycle internal combustion engine, exhaust gases may blow back into the combustion chamber through the scavenging port due to pressure differentials set up by the operational cycle of the intake port.
In order to improve the output performance of such internal combustion engines, it is desirable to provide some means to prevent gas back-flow. The prior art has, to date, dealt with the problem of gas-back flow by employing an auxiliary intake or back-flow prevention valve slidably carried on a conventional intake poppet valve. For example, U.S. Pat. No. 3,903,855 discloses a back-flow intake valve normally spring-biased into closed position upstream of the intake poppet valve. The back-flow prevention valve is opened by pressure in the intake passage exceeding the pressure in the combustion chamber during the time interval when the intake poppet valve is open. By biasing the back-flow prevention valve in a normally closed position, the mass of the back-flow prevention valve functions as additional resistance against the intake flow of air-fuel mixture from the intake passage during the intake stroke and therefore lowers the intake efficiency of the engine. In the German Pat. No. 460,151 a back-flow prevention valve is disclosed with no biasing mechanism whatsoever and thus the intake flow of air-fuel mixture from the intake passage to the combustion chamber is once again faced with resistance from the mass of the back-flow prevention valve.
The present invention improves upon the intake valves of the prior art designed to prevent back-flow of gases in internal combustion engines. The present invention effectively combines a back-flow prevention valve with a biasing arrangement to result in a commercially-acceptable intake valve which not only effectively prevents back flow of gases into the intake passage of an internal combustion engine but also minimizes resistance against the intake flow of air-fuel mixture during the intake stroke of the engine and therefore maximizes the intake efficiency of the engine.
Accordingly, it is a prime object of this invention to provide a new and improved intake valve mechanism for preventing the back-flow of gases from the combustion chamber out the intake port.
It is a further object of this invention to provide an intake valve mechanism for preventing back-flow of gases that is simple in construction and easy to manufacture.
Another object of this invention is to provide an intake valve mechanism for preventing back-flow of gases that is designed to maximize the intake efficiency of the engine.
Still another object of this invention is to provide an intake valve mechanism for preventing back flow of gases that is designed to minimize the volume of back flow.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.